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Structure and Optical Properties of Layered Perovskite (MA)2PbI2-Br(SCN)2 (0 ≤ x < 1.6)
Takafumi Yamamoto1,2, Iain W H Oswald3, Christopher N Savory4,5
1Laboratory for Materials and Structures, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
Abstract:
The layered perovskite (MA)2PbI2(SCN)2 (MA = CH3NH3+) is a member of an emerging series of compounds derived from hybrid organic-inorganic perovskites. Here, we successfully synthesized (MA)2PbI2-Br(SCN)2 (0 ≤ x < 1.6) by using a solid-state reaction. Despite smaller bromide substitution for iodine, 1% linear expansion along the a axis was observed at x ∼ 0.4 due to a change of the orientation of the SCN- anions. Diffuse reflectance spectra reveal that the optical band gap increases by the bromide substitution, which is supported by the DFT calculations. Curiously, bromine-rich compounds where x ≥ 0.8 are light sensitive, leading to partial decomposition after ∼24 h. This study demonstrates that the layered perovskite (MA)2PbI2(SCN)2 tolerates a wide range of bromide substitution toward tuning the band gap energy.
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